In prior-art implementations, chip stock has been fed into the chip refiner at a constant rate. Because of the variations in the chip stock consistency and chip size, this method is incapable of producing refined stock at a constant quality.
Also, controlled systems are known in the art in which chip stock is fed using a variable-speed motor. In one of these methods, feed rate is controlled by regulating the input power to the chip refiner from the power source to a constant level. Even if a constant load by the refiner on the power source is maintained, uneven quality of the refined stock will result, due to variations in chip stock consistency and moisture content. In another method using control means, chip stock is fed into the chip refiner at controllable set rate by measuring the output rate and refined stock consistency from the chip refiner, computing the product of these measurement variables which is relative to mass flow rate, and the obtained mass flow rate is used as the input variable for the control loop of the input feed rate. Because of the technical difficulties in deriving the value of the mass flow rate, the control response of the method is rather slow. Consequently, an unsatisfactory quality of refined stock results therefrom.